The forming rollers of a roller forming machine are arranged in mating pairs, with the two rollers of each pair configured to produce a predetermined lateral deformation of an elongated sheet metal workpiece passing lengthwise between them. Normally such a machine comprises several pairs of forming rollers, located at spaced intervals along the path traversed by the workpiece and cooperating to impart a progressive deformation or bend to the workpiece as it moves through successive forming roller pairs along that path.
Although an endless variety of transverse profiles can be imparted to workpieces with a roller forming machine, the production of every different profile requires the use of a different set of forming rollers. For versatility, most roller forming machines are designed for interchangeable forming rollers, but changing forming rollers for running a different type of workpiece is nevertheless time-consuming.
Each forming roller is detachably fixed to a forming roller shaft, and the two roller shafts for each forming roller pair have their opposite end portions journaled in bearings that are mounted in a pair of upright support stands, one at each side of the machine frame. For driving the roller shafts in rotation, a line shaft extends along one side of the frame, at the outboard side of the support stands at that side. In heretofore conventional roller forming machines, gears have been secured to the roller shafts near their ends adjacent to the line shaft, for drivingly connecting the roller shafts with the line shaft and for constraining the two roller shafts of each pair to rotate at like speeds but in opposite directions. The support stands at the ends of the roller shafts remote from the line shaft were detachably secured to the machine frame so that upon their removal the forming rollers could be slid axially off of and onto the roller shafts.
Thus, interchange of forming rollers for conversion to production of a different type of workpiece has involved, among other things, removal and reinstallation of all of the support stands along the side of the machine remote from the line shaft and therefore has usually taken a time measurable in hours. Heretofore a roller forming machine has been out of production all during the time needed for such a changeover.
Where production runs are long for each different type of workpiece, the down time needed for occasional conversion by interchange of forming rollers is not of great consequence because it is small in proportion to production time. But with the increasing adoption of "just in time" production scheduling, intended to minimize inventories of partly finished materials, there has developed a need for short but economical production runs. For this, reduction of down time to an absolute minimum is imperative.
In the present state of the art it does not seem probable that the time required for interchange of forming rollers on the roller shafts of a roller forming machine can be materially reduced, especially in the case of the high-performance, heavy duty roller forming machines typically needed in situations where short runs and frequent conversions are the rule.
An obvious but impractical solution is to have two roller forming machines available, each to be used for production while the other is down for conversion. Aside from the unduly high capital investment in two such machines--each rather expensive in itself--and in the valuable floor space they would occupy, there is the further consideration that a roller forming machine is usually present as one element of a processing line that comprises other machines such as a punch press, a cutoff machine, a conveyor, and so on. Since the roller forming machine must be physically aligned with the other machines with which it cooperates, to provide for smooth flow of materials along the processing line, resort to a second roller forming machine for minimizing down time would practically compel the uneconomical provision of a second complete processing line that would be out of operation during about half of the time.
In one attempt at reducing the down time required for conversion of a roller forming machine, the machine has been constructed as a stationary main frame arranged to receive a set of removable forming roller subassemblies, each of which comprised a subframe carrying a few pairs of roller shafts, their forming rollers, their support stands and their gearing. The user of the machine had two or more sets of such forming roller subassemblies that were interchangeable with one another on the stationary main frame, each set having forming rollers adapted to produce a particular type of workpiece. The drive means for the roller shafts, comprising a line shaft driven by a motor, was permanently mounted on the main frame. For conversion from one type of workpiece to another, the drive means was disconnected from the subassemblies then mounted on the main frame, and each subassembly in turn was lifted off of the main frame by means of an overhead crane, which carried it away to storage. The crane returned with a replacement subassembly, adapted for a new workpiece to be produced, and lowered it into position on the main frame. The drive means then had to be connected with the replacement subassemblies to prepare the machine for beginning the new production run.
Disconnection of the subassemblies from the drive means was a time consuming operation involving individual disconnection of splined elements; and reconnection of the new subassemblies with the drive means took even longer. In addition, a substantial amount of time was taken up by the several back and forth trips of the overhead crane. Of course the need for an overhead crane--which was not always available--was an obvious disadvantage. Although there was some saving in down time, the time required for interchange of subframes was by no means short, so that the obviously high cost of this solution was not in all cases justified by the results obtained with it.